This invention relates to optical transmission elements and cables in general and more particularly to an improved protective casing for optical fibers and optical cables.
Recently cables have been developed for the transmission of light waves using fiber optics. These cables, referred to as optical cables, are used for the transmission of control pulses or may be used in the field of communications engineering, i.e. in telephone systems, etc. The main component of the optical cables are the glass fibers or fiber optics which serve to guide the light beams. When designing optical cables, the mechanical properties of the glass fibers must be taken into consideration. In other words, the glass fibers must be protected, particularly from mechanical stresses as compression, tension and flexural stresses.
Optical conductors are known in which the transmission element itself, i.e. the glass fiber or fiber bundle, is surrounded directly by a covering of plastic. To a certain degree such a covering performs a protective function. On the other hand, it gives an increase in the thickness of the optical transmission element with the object of better handling in processing it into a cable. However, such a covering does not provide effective protection of the transmission element with respect to mechanical stresses. For one thing, the material of the protective covering does not give optimum protection against mechanical stresses such as tensile stresses, impact and flexural stresses and furthermore there is a mechanical coupling through the protective covering of the transmission element to the other elements of the cable core.
It is also known in one cable design to protect the optical transmission element against mechanical stresses by arranging the optical transmission elements on a carrier element comprising a central stress relief element having a star-shaped profiled body applied thereon. The profiled body along with an outer covering forms chambers into which the optical transmission elements are arranged. They are secured in place on the profiled body at spacings by means of special tapes. To provide outer protection, the star-shaped carrier element, after being wrapped with a serving material, is surrounded with an aluminum sheath and protective jacket of polyethylene. Through securing of the optical transmission elements onto the carrier element at spacings, a relatively strong mechanical coupling is established between the optical transmission elements and the tension-proof elements of the cable. This design can also cause problems.
Thus, none of these prior art designs is particularly satisfactory. What is needed is a protective arrangement in which the protection of the optical elements is provided through an appropriate design of the protective casings of the optical conductors themselves.